Star image identification means in planetariums have hitherto involved projection onto the viewing screen of an arrow image pointing to the star image to be identified, or by the projection of a circle image so positioned as to encircle the star image to be identified.
Such prior identification means require complex electrical circuits, often with contact slip-rings as well as mirrors reflecting light rays to produce identification images upon a viewing screen in proximity to the star images to be identified.
In such prior arrangements, the means for projecting the arrow or circle have been additional to the means for projecting the star image and have necessarily been located laterally of the beam of light which projects the star image. Such prior arrangements are fraught with great difficulty both in providing the necessarily additional projecting means and in the need for complex mechanisms for spotting the arrow or circle on the screen in proper relation to the star image to be identified.
All references in this specification and in the accompanying claims to a "star" or a "star image" should be understood to comprehend, also, a planet or a planet image.